Process for the continuous manufacture of viscose products



Patented Sept. 4, 1951 PROCESS FOR THE CONTINUOUS MANU- FACTURE OF VISCOS E PRODUCTS Robert Levison, Ede, and Barend Jan Blomberg, Velp, Netherlands, assignors to American Erika Corporation, Enka, Delaware 0., a-corporation of No Drawing. Original application March 16, 1949, Serial No. 81,844. Divided and this application December 21, 1950, Serial No. 202,149. In the Netherlands May '7, 1948 4 Claims. (01. 1854) This application is a division of our application Serial No. 81,844, filed March 16, 1949.

The present invention relates to a continuous process for manufacturing viscose products, and more particularly to a proces in which freshly formed viscose threads are aftertreated by passing a large number of such threads through treating zones or in parallel relationship and in a substantially linear direction through successive treating baths at such high speeds that the treatment time in each individual zone or bath is only a few seconds.

When manufacturing products from viscose, such as rayon, artificial horsehair, ribbons, films, and the like, a viscose solution is forced through spinning nozzles or slits into coagulating baths, wherein the product are coagulated and partially regenerated. The products are thereafter drawn from the coagulating bath and subjected to various after treatments for the purpose of obtaining an end-product consisting of pure cellulose hydrate, which has been completely freed of residues formed during the decomposition of the viscose and freed from spinbath constituents and from sulphur and other impurities.

In manufacturing viscose rayon according to the discontinuous process in which the threads are coagulated and partially regenerated in the spinbath, the threads containing the acids and salts from the spinbath are collected on bobbins or in pots and thereafter allowed to remain for several hours so that complete regeneration of the cellulose. or better said, the decomposition of the xanthate is elfected. In certain cases,

after the threads have left the spinbath they are i subjected to further regeneration in a second bath containing sulphuric acid, and, if desired, sodium sulphate, and then collected on bobbins or in pots. However, even in this case it is necessary to store the packages for some time in order to assure complete decomposition of the xanthate.

After the packages have been stored for a sufficient time, they are pressure and/or vacuum washed with water to remove the acid and salts and thereafter desulphurized, and if necessary, bleached, and finally dried. In this discontinuous process since the threads have been completely regenerated prior to washing, desulphurizing and bleaching, no problem existed with respect to the desulphurizing and bleaching operation. The threads were properly desulphurized and bleached to a pure white product.

In the most widely used continuous system for i the manufacture and aitertreatment of viscose threads, the threads are subjected to the various aftertreatments by passing them around threadstorage, thread-advancing devices in a multiplicity of convolutions. During their passage around the devices they are subjected to the required treatments, such as, partial decomposition, final decomposition, desulphurizing, bleaching and drying. However, even in this type of continuous process the time i not critical because the individual treatment operations consume, for example, from 40 seconds to one minute, which, if acid and washing treatments are given, are sufficient to effect proper desulphurization and bleaching.

In all of the known discontinuous processes, and the continuous processes with thread storage, during the preparation and aftertreatment of threads spun from viscose the decomposition of the xanthate was advanced by the liquid carried along by the thread from the original spinbath; when the decomposition seemed insuiiicient, complementary acid baths were employed. Since, in these processes, time was no factor, it was not discovered that the sodium sulphate. used in the baths or formed during the decomposition of the xanthate had a disadvantageous; effect on the decomposition of the thread, and; therefore no steps were taken to remove the; salts. As a matter of fact, it i well. known that freshly spun threads which are only par-- tially decomposed require a certain amount of salt in the acid baths to prevent turgor-action, which i caused by swelling of the interior of the filaments to a greater extent than the exterior because of a skinlike formation at the exterior of the filaments. This turgescent swelling results in the threads bursting open and sticking together upon subsequent treatment with water or dilute acid baths free of salts.

A more recently developed continuous system for manufacturing rayon products is described and claimed in U. S. Patent No. 2,334,325, U. S. Patent No. 2,459,254, U. S. application Serial No.

18,408, now U. s. Patent No. 2,539,980 and U. s.

application Serial No. 713,905 now U. S. Patent No. 2,513,057 (both assigned to the same assignee as the present application), French Patent No. 884,760 and British application Serial No. 9,912/47. This group of patents and applications relate to a high speed continuous process in which the threads are passed in parallel, linearly through successive treating baths at high rates of speed, for example, from meters per minute to meters or more per minute. This type of to provide a bath travel of over several meters.

during any one of the treating, operations.

Therefore, I the individual treating times, are limited to only a few seconds, for example, 3 or 4 seconds and certainly not over seconds; Due.

to the short treatment times inherent inthis process, the threads are insufficientlyregener ated, i. e., the xanthate is not completely decompos d, and therefore when thetnread. is passed through the desulphurizing.bathiononlya few;

seconds it was found to be incompletely. .desu1-; phurized and consequently residual sulphur remains in the finished product whereby ayellow discoloration occurs.

the antha H H I salts should be'washed out, because the presence 'of sajlt will.fappreeiably delay further decomposi tionjof; the last remaining very small amounts" of xanthate residues.

Primarily ,it was determined that the principal after treatments, vizQ, complete decomposition of the ,Xanthate and'desulphurization are dependent onjeach other, in that, the desulph'urizing proce'eds more completeiyin direct relation to the degree of decomposition of the xanthate remain ing inthethreads. If the decomposition of the x'anthate'is not substantially complete or below a definite predetermined limit then the desulpl'iuriaing operation cannot be performed properly, i. e., all of the sulphur cannot be removed in the time allotted and this residual sulphur will show infthe final product which willlower' the quality thereof. On the other hand, as soon as the'decomposition oith'e xanthate has reached a very advanced stage, e. g., the xanthate ratio falls below .003 'or preferably below .002, the desulphurizationcan be carried out in a reliable man'- ner'that is completely satisfactory for all practical purposes. 'Prior to "the present-invention when usingone of the normal' desulphurizing agents such as sodium sulphide, it has not beenpossible'to remove allof the sulphur in 'a' con tinuous process involving highspeed treating operations. Because of this,- continuous spinning of this type has not been practical, and h'as'thereforebeen slow in its commercial development. 1 It is therefore the object of the present invention to provide a particular type of after-treatment or series of aftertreatments that can be utilized effectively in this more recently developed continuous spinning system.

Another object of the invention is to decompose the residual xanthate in the freshly spun threads in several seconds but so completely that the threads can be immediately desulphurized so thoroughly within a very few seconds that no sulphur deposits can be detected in the final product.

A still further object of the invention is to employ certain materials in the aftertreatment baths that will accelerate the decomposition of the last remaining xanthate in the thread to quickly lower the Xanthate ratio below a critical point, i. e., below .003 or .002. (The xanthate ratio, i. e., the ratio of the number of residual Xanthate groups to the total number of cellulose groups (cameos) is determined by any of the While it is necessary "to eysa r a n manate? s l p esent during he decomposition," as soon as the decomposition of 1 a has reached an advanced'statethe means oila hot dilute acid bath containing sul- 'well known chemical methods.

One suitable determinative method is described in Leroy H. Smith, Synthetic Fiber Developments in Germany 1946, pages 201-204.)v i

Other objects and advantages of the invention will become apparent from the following detailed description.

. In,practicing acoording to the present invention and utilizing high spinning speeds in which individual treatments are effected in less than 10 seconds, it. was first determined that after the thread has been coagulated and partially regenerated in 'a normal sulphuric acid, salt-containing spinbath, the further decomposition of the xanthate can be effectively accomplished by phuric acidinarange of 0.5%-6.0% and correspondingly..1.0.%. to 10% sodium sulphate, said bathheing maintained at a temperature in the range of 60 to C.

By passing the thread through such a hot dilute acid-bath, itcan be substantially completely regenerated inthree or fourseconds, although a small amount of residual undecomposed Xanthat e (X. R." about 0.02)- does remain in the. thread which must be removed priorto desulph'uri'zation. Ithas been determined thatthe' remaining amount of undecomposed xanthate can be removed orthe xanthate ratio can be reduced below 1003 in 3 or 4 secondsafter a th0rough washing toremove the salts from the thread, by immediately passing the" "thread through a pure dilute sulphuric acid bath. (not: diluted spinbath) containing sodium sulphate substantially below the bisulphate ratio, i. e., for every mol of sulphuric acid, less than 1 mol of. sodium sulphate is used. This means that the molecular ratio of sodium sulphate to sulphuric acid is substantially less than-l': l. Therefore; it is necessary, for example, when using 3% sule. ph'u'ric' acid to. take precautions that thewsalt. content can neverbe as much as 4.3.%..sodium. sulphate. Particularly good rsultsifhaveilbeeni achieved when using 4% sulphuric acid.and'2.%.. or less sodium sulphate, which corresponds; to a molecular ratio of 2.8:1'. In. this. way .thesalt content can alway be maintained. ata predetermined value below the bisulphaterati'o bee:

cause the threads being first washed andthen. treated with-"a. pure. sulphuric acid as distin: guished from a dilute spinbath, the salt content. can never increase as in .the..case. .where. the thread containing. salts is allowed. to,v pass; through the treatment bath wherein the, salt, content continually builds up. i

Asan alternative procedure for treating; the. thread in a .dilute sulphuric acid bath cOntaiIling sodium sulphatebelowthej bisulphate ratio for the purpose .of removing theremaining amount of .undecomposedxanthate, the thread can be treated ina bath containing. certain oxidizing decomposing. agents, such as H202, K25 O H0103, H0104, NaOCl, NaClOz, NaNO2, p r t solutions of. sodium hypochlorite or sodium chlorite were. found to be particularly eife'ctive When using solutions of sodium hypochlorite, the best concentration range is between 0.5% and 2%, and the solutionismaintained at room tfil'l'l-w perature. 'Wheniusing sodium chlorite, .prefere ably in acid solutions, the best results are ;..at-. tainedat higher. temperature, for example 70? C. although the concentration is lower, viz., 0.2% to 1% The steps involved in the present invention. are as followsz A multiplicity of threads are extruded through spinnarets into a normal coagulating spinbath containing sulphuric acid and salts thereof and are then passed in parallel relationship linearly through several baths in the sequence, first, either to a hot dilute sulphuric acid bath having an acid concentration of from 0.5% to 6% and sodium sulphate in a concentration of 1.0% to said bath being maintained at a temperature of from 60 to 95C., or the threads are subjected to further regeneration by the spinbath liquid retained in the threads, but in either case the xanthate ratio can only be lowered to about 0.02 which is insufficient to effect complete desulphurization in the time available. or other suitable treating liquid to remove the salts therefrom. Next the threads are passed through a dilute pure sulphuric acid bath containing sodium sulphate below the bisulphate ratio or through a bath containing an oxidizing agent. Thi treatment lowers the xanthate ratio below the critical point, namely, below .002 or at least below .003. The thus treated threads are again washed by passing them through a water bath, and are then immediately desulphurized and bleached in successive baths, and finally dried. This process is a continuous one from the beginning to the end, and each of the treatment operations are effected in 3 or 4 seconds, or less, but in any case, never more than 10 seconds.

The invention is not limited to normal rayon such as 2.5 and 5 illiament denier, but is also applicable to the preparation of thicker products made from viscous such as horsehair, ribbons, and films, and when the expression threads is used in the claims it is intended to cover these other said products.

Obviously, various modifications may be made without departing from the spirit and scope of the invention, e. g., it may not be necessary to utilize the washing step between the last decomposing bath and the desulphurizing bath, provided some equivalent means is used to remove the acid such as by an expressing operation.

What is claimed is:

1. A process for the continuous manufacture of viscose threads which comprises extruding a multiplicity of threads through spinnerets into a coagulating bath containing sulphuric acid and salts thereof, passing the threads in parallel relationship linearly through a second bath at such a high speed that the time of passage through the bath is less than ten seconds thereby lowering the xanthate ratio below 0.02, which is insufficient to permit subsequent complete desulphurization, said second bath being maintained at a temperature in the range of 60 C.-95 C. and containing a lower concentration of acid and salt than that of the first bath, washing the threads free of salts, decomposing the remaining xanthate in the threads to a xanthate ratio below 0.003 by treating them in a solution containing an oxidizing agent, and again washing the threads and effecting substantially complete desulphurization, each of said treatments being effected in less than ten seconds.

2. A process for the continuous manufacture The threads are then washed with water .6 Of viscose threads which comprises extruding a multiplicity of threads through spinnerets into a coagulating bath containing sulphuric acid and salts thereof, passing the threads in parallel relationship linearly through a second bath at such a high speed that the time of passage through the bath is less than ten seconds thereby lowering the xanthate ratio below 0.02, which is insufficient to permit subsequent complete desulphurization, said second bath being maintained at a temperature in the range of C. C. and containing a lower concentration of acid and salt than that of the first bath, washing the threads free of salts, decomposing the remaining xanthate in the threads to a xanthate ratio below 0.003 by treating them in a solution containing an oxidizing agent of the class consisting of H202, 'KzSzOs, H0103, H0104, NaOCl, NaClOQ, and NaNOz, and again washing the threads and effecting substantially complete desulphurization, each of said treatments being eifected. in less than ten seconds.

3. A process for the continuous manufacture of viscose threads which comprises extruding a multiplicity of threads through spinnerets into a coagulating bath containing sulphuric acid and salts thereof, passing the threads in parallel relationship linearly through a second bath at such a high speed that the time of passage through the bath is less than ten seconds thereby lowering the xanthate ratio below 0.02, which is insufficient to permit subsequent complete desulphurization, said second bath being maintained at a temperature in the range of 60 C.-95 C. and containing a lower concentration of acid and salt than that of the first bath, washing the threads free of salts, decomposing the remaining xanthate in the threads to a xanthate ratio below 0.003 by treating them in a solution containing sodium chlorite, and again washing the threads and efiecting substantially complete desulphurization, each of said treatments being effected in less than ten seconds.

4. A process for the continuous manufacture of viscose threads which comprises extruding a multiplicity of threads through spinnerets into a coagulating bath containing sulphuric acid and salts thereof, passing the threads in parallel relationship linearly through a second bath at such a high speed that the time and passage through the bath is less than ten seconds thereby lowering the xanthate ratio below 0.02, which is insufficient to permit subsequent complete desulphurization, said second bath being maintained at a temperature in the range of 60 C.-95 C. and containing a lower concentration of acid and salt than that of the first bath, washing the threads free of salts, decomposing the remaining xanthate in the threads to a xanthate ratio below 0.003 by treating them in a solution containing sodium hypochlorite, and again washing the threads and effecting substantially complete desulphurization, each of said treatments being effected in less than ten seconds.

No references cited. 

1. A PROCESS FOR THE CONTINUOUS MANUFACTURE OF VISCOSE THREADS WHICH COMPRISES EXTRUDING A MULTIPLICITY OF THREADS THROUGH SPINNERETS INTO A COAGULATING BATH CONTAINING SULPHURIC ACID AND SALTS THEREOF, PASSING THE THREADS IN PARALLEL RELATIONSHIP LINEARLY THROUGH A SECOND BATH AT SUCH A HIGH SPEED THAT THE TIME OF PASSAGE THROUGH THE BATH IS LESS THAN TEN SECOND THEREBY LOWERING THE XANTHATE RATIO BELOW 0.02, WHICH IS INSUFFICIENT TO PERMIT SUBSEQUENT COMPLETE DESULPHURIZATION, SAID SECOND BATH BEING MAINTAINED AT A TEMPERATURE IN THE RANGE OF 60* C.-95* C. AND CONTAINING A LOWER CONCENTRATION OF ACID AND SALT THAN THAT OF THE FIRST BATH, WASHING THE THREADS FREE OF SALTS, DECOMPOSING THE REMAINING XANTHATE IN THE THREADS TO A XANTHATE RATIO BELOW 0.003 BY TREATING THEM IN A SOLUTION CONTAINING AN OXIDIZING AGENT, AND AGAIN WASHING THE THREADS AND EFFECTING SUBSTANTIALLY COMPLETE DESULPHURIZATION, EACH OF SAID TREATMENTS BEING EFFECTED IN LESS THAN TEN SECONDS. 